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Writing Ionic Formulas
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Ionic Compounds Things you should know: Ionic = metal-nonmetal combo of elements Metal: loses e- to become stable; positive ions Nonmetal: gains e- to become stable; negative ions The charge value (1, 2, or 3) depends on how many e- were lost or gained. The # lost or gained was the # needed to be “full”.
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Predicting Charges on Ions KNOW THESE !!!! +1 +2 +3 -3 -2 -1 0
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Method One: electron dot diagrams The # of dots shown = # of valence e-. Column # = # of valence e-. e- are gained or lost in the # needed for each atom/ion to be stable.
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e- dot diagrams for some common elements
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Use e- dot diagrams to show the transfer of e- to make the metal and nonmetal atoms stable. e- dot diagram for Potassium (K)e- dot diagram for oxygen (O) Transfer of e- to form potassium oxide
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Writing the Formula If the ratio is 1:1, no subscript is needed. Ex: sodium chloride = NaCl If the ratio is NOT 1:1 use a subscript for each element which has more than 1 ion involved in the transfer. Ex: potassium oxide = K 2 O
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Your Turn! What is the formula of barium iodide? Show the e- dot diagram of each element. Show the transfer of e-. Write the formula based on the ratio of the ions.
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Barium Iodide e- dot diagram for Barium (Ba)e- dot diagram for iodine (I) Transfer of e- to form barium iodide
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Formula BaI 2
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Method 2: using charges of the ions Ion charge for Aluminum (Al)Ion charge for chlorine (Cl) “Adding” the ions to get a neutral compound
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The formula AlCI 3
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Your Turn! What is the formula of lithium sulfide? Determine the ion charge of each element. Determine the # of each ion needed to form a neutral compound. Write the formula based on the ratio of the ions.
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The Formula Li 2 S
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Transition Metals Transition metals = B column elements Charge can vary. It may be: +1, +2, +3, or +4. A number in parentheses following the name of the metal gives the ion charge. Ex: Iron (II) = Fe +2 Iron (III) = Fe +3
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Teacher Example What is the formula of chromium (III) sulfide? Ion charge for Chromium (Cr)Ion charge for sulfide “Adding” the ions to get a neutral compound
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The formula Cr 2 S 3
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Your Turn! What is the formula for silver (I) chloride?
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The formula AgCI
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Polyatomic Ions Not all ionic compounds are composed of metal and nonmetal elements. What?!?! All ionic compounds ARE composed of positive and negative ions. Some ions are composed of 2 or more elements. Poly = “many” Atomic = refers to atoms
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Polyatomic Ions-continued = a group of atoms covalently bonded together that has a net charge. Examples: NH 4 + Ammonium C 2 H 3 O 2 - Acetate CN - Cyanide O 2 2- Peroxide NO 3 - Nitrate NO 2 - Nitrite SO 4 -2 Sulfate SO 3 -2 Sulfite
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Together, the group has a charge. Like a molecule, the O and H atoms stay bonded together and act as one particle. 1–1– H O
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O Cl O 1–1– One chlorine atom and two oxygen atoms covalently bonded, together carrying a 1- charge ClO 2 -
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Writing a formula that contains a polyatomic ion Use the charge method. “Adding” the charges of the ions, the compound must be neutral. Compound: Magnesium hydroxide
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Magnesium hydroxide Ion charge for Magnesium (Mg)Ion charge for hydroxide (OH-) “Adding” the ions to get a neutral compound
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The formula Mg(OH) 2
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Your Turn! Write the formula for lithium phosphate.
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The formula LiPO 4
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Let’s Put It All Together Transitional metal and Polyatomic Ion What is the formula of chromium (III) sulfate? Ion charge for Chromium (Cr)Ion charge for sulfate “Adding” the ions to get a neutral compound
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